November 21, 2013

A New Apple iPhone 5S Touch ID Patent Surfaces

Patently Apple was first to reveal Apple's Touch ID patents in Europe just days before Apple unveiled this new feature in the iPhone 5S in September. Today, the US Patent & Trademark Office published another Touch ID related patent application from Apple that covers the circuits and packaging for fingerprint sensors.

Apple's Patent Background

Capacitive sensing of fingerprints provides for collection of fingerprint information in response to distinct measures of capacitance between, on the one hand, one or more capacitive plates in a fingerprint recognition sensor, and on the other hand, ridges and valleys of a user's finger (such as the epidermis of the user's finger, or possibly, subdermal layers of the user's finger).

It sometimes occurs that measurements of capacitance involve introduction of electric charge on the epidermis of the user's finger. This can have the effect that only a small amount of charge can be introduced without the user feeling the charge, sometimes as a tingling or other noticeable effect on the epidermis of the user's finger.

It sometimes occurs that measurements of capacitance involve relatively small differences in capacitance between, on the one hand, the capacitive plates of the fingerprint recognition sensor, and on the other hand, the ridges and valleys of the user's finger. For example, this would involve placing the user's finger as close as possible to the capacitive plates. This can have the effect of limiting the design flexibility for the fingerprint recognition sensor.

It sometimes occurs that measurements of capacitance involve positioning of the user's finger with respect to the fingerprint recognition sensor. For example, the user's finger might have to be placed within a conductive ring, significantly limiting the size and position of the fingerprint recognition sensor. This can also have the effect of limiting the design flexibility for the fingerprint recognition sensor.

It sometimes occurs that measurements of capacitance involve capacitive coupling with a portion of the user's finger other than the epidermis. For example, capacitive coupling (or other fingerprint recognition sensing) might involve as a subdermal layer of the user's finger.

This might involve introduction of a relatively greater electric charge to conduct that capacitive coupling. As described in part above, this can have the effect that the user might feel the charge, sometimes as a tingling or other noticeable effect in a portion of the user's finger.

Each of these examples, as well as other possible considerations, can cause difficulty for the fingerprint recognition sensor, and for the device incorporating the fingerprint recognition sensor (such as a computing device using fingerprint recognition for authentication). The fingerprint recognition sensor might be limited in size, or position, or in whether it can be relatively easily incorporated with other elements of the device incorporating the fingerprint recognition sensor. For a first example, this can have the effect that the fingerprint recognition sensor might not be easily incorporated into some types of devices (such as relatively small devices like smartphones and touchpads). For a second example, this can have the effect that the fingerprint recognition sensor might be required to be relatively fragile or otherwise subject to unwanted design constraints.

Apple's Touch ID

Apple's invention provides techniques, including circuits and designs, which can receive information with respect to fingerprint images, and which can be incorporated into devices using fingerprint recognition. For example, the fingerprint sensor can be disposed beneath a control button or display element, for fingerprint recognition and authentication while the device is being operated by a user.

In one embodiment, techniques include providing a fingerprint recognition sensor disposed underneath other elements, but which is still disposed relatively close to the user's finger when fingerprint recognition is conducted. Circuits can be disposed underneath a button or underneath a display element, but with reduced amount of distance between one or more capacitive plates and the user's finger. For some examples, circuits can be disposed underneath a device element, with the fingerprint recognition sensor circuit itself having reduced vertical spacing by one or more of (1) coupling the fingerprint recognition sensor circuit using bonding wires disposed through one or more vias cut through a silicon wafer from the top of the circuit, (2) coupling the fingerprint recognition sensor circuit using bonding wires disposed through one or more trenches cut through a silicon wafer from an edge of the circuit, (3) encapsulating the fingerprint recognition sensor circuit in plastic molding which is at least partially removed, and (4) coupling the fingerprint recognition sensor circuit to other circuits using solder elements, such as encapsulated solder balls or compressed solder elements.

In one embodiment, circuits may embody or employ techniques which use elements of the device to aid the fingerprint recognition sensor in fingerprint recognition. For some examples, circuits can be disposed using one or more device elements, with the one or more device elements assisting the fingerprint recognition sensor circuit by one or more of (1) coupling capacitive elements to a side of the device or near a button or other device element, (2) printing circuit elements to assist the fingerprint recognition sensor, or included in the fingerprint recognition sensor, on an underside of a button or other device element, (3) coupling fingerprint recognition sensor circuit elements to a button or other device element which improves coupling an electric field of the fingerprint recognition sensor, such as an anisotropic element including sapphire or another substance, and (4) using a transparent or translucent button or other device element to perform optical sensing or infrared sensing in addition to capacitive sensing, to assist or be included in the fingerprint recognition sensor circuit.

In one embodiment, circuits include techniques which use elements of the device including the fingerprint recognition sensor circuit to assist the user when using the fingerprint recognition sensor. For some examples, circuits can be disposed using a device element, with the device element being disposed to assist the user by one or more of (1) using a recessed shape formed at least in part by a button or other device element to help position the user's finger for fingerprint recognition when using the fingerprint recognition sensor circuit, and disposing the fingerprint recognition circuit underneath the button or other device element, and (2) disposing the fingerprint recognition circuit over a touch-responsive push button to provide tactile feedback.

Apple's invention is covers the iPhone 5S Touch ID Home Button fingerprint scanner which Apple notes may apply to future products such as the iPad, iPod and personal computers such as the MacBook and iMac. In some designs, the fingerprint sensor is disposed beneath a control button or display element, so that fingerprint recognition and authentication can be performed while the device is being operated by a user.

Apple's fingerprint sensor itself may utilize a grid of capacitive elements for capturing the fingerprint image, or an optical sensor or other suitable fingerprint imaging technology. A control circuit can also be provided, for example a control button or switch element responsive to touch or pressure, or a touchscreen control system responsive to proximity and (multiple) touch positioning. In some designs, the fingerprint sensor is utilized in combination with a control button or display element formed with an anisotropic dielectric material, such as sapphire.

The examples and embodiments described herein generally disclose various structures and methods for packaging a sensor, such as a capacitive sensor. Some embodiments incorporate various placements of the sensor, structure surrounding a sensor, connection structures (electrical, physical, or both), and techniques for enhanced sensor imaging, sensor retention, and guiding a user's finger to a proper location above a sensor, where the sensor itself cannot be seen.

Apple's patent FIG. 1 illustrated below shows us a conceptual drawing of a fingerprint recognition sensor included in a portion of an iPhone. An exploded view figure of a portion of the iPhone shows an assembly of parts disposed to form the fingerprint recognition sensor circuit and position of the sensor circuit below the push button/Home button.

The recessed shape may likewise be at least partially formed by a chamfer in the ground ring. In one embodiment, the button 104 can be made of one or more of the following materials, or equivalents thereof: aluminum oxide, glass or chemically treated glass, sapphire, a chemically treated compound having at least some characteristics thereof, or another compound having similar properties.

The lens 112 is disposed within a ground ring 114. In one embodiment, the ground ring can be used to shield electromagnetic effects, with the effect of providing capacitance isolation or other electromagnetic isolation. The ground ring is shown in the figure as having a cylindrical edge which holds the lens, and a base plate which can be aligned or oriented within the device 100 when the assembly is constructed.

The button 104 is disposed above and coupled to a fingerprint recognition sensor 102 circuit. In one embodiment, the fingerprint recognition sensor circuit is relatively rectangular, with the effect of being able to sense an a two dimensional (2D) image of the user's fingerprint. However, in alternative embodiments, the fingerprint recognition sensor circuit can be disposed on another shape, such as a circular or hexagonal shape which might also be suited to receiving 2D fingerprint image information.

Apple notes that their fingerprint recognition sensor circuit might work in combination or conjunction with elements which perform optical sensing, infrared sensing, or other sensing of the user's fingerprint, and which themselves might be coupled either to the epidermis of the user's finger, to a subdermal portion of the user's finger, or to some other feature representative of the user's fingerprint.

In patent FIG. 3 we see a set of ridges and valleys 302 of the user's fingerprint are shown disposed above the button assembly with the ridges and valleys 302 having the property that ridges of the user's fingerprint are relatively closer to the external surface of the home button while valleys of the user's fingerprint are relatively farther away from the external surface of the home button.

Apple's patent figure 4B is a top view of the fingerprint recognition sensor silicon wafer.

The use of Sapphire

Apple's patent FIG. 7 generally shows a sample crystal lattice structure 700 for sapphire, with the critical plane 702 (in this case, the C-plane) oriented as a top surface.

Apple states that it should be appreciated that anisotropic dielectric materials may be used to form one or more layers above the capacitive sensor, such as a cover glass or button surface layer.

Anisotropic dielectrics may reduce blurring that is otherwise introduced by distance between a capacitive fingerprint sensor array and a finger's surface (or subsurface). For example, orienting a sapphire layer covering or extending between the finger and capacitive sensor array may enhance imaging.

The sapphire layer may be oriented such that one of its axes perpendicular to its C-plane (such as the M-plane and A-plane) extends between the sensor imaging array and the surface to be contacted by, or near, a finger that is to be imaged. Generally, sapphire axes perpendicular to the C-plane may have a higher dielectric constant than directions parallel to the C-plane and thus enhance capacitive sensing and/or imaging. Although either mono-crystalline or polycrystalline sapphire may be used in various embodiments, certain embodiments may specifically employ mono-crystalline sapphire.

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